The invention relates to wells of all types which require sand control but particularly to deep wells such as those used for producing oil and/or gas. In deep wells it is extremely costly to complete the well in the producing zone by the conventional techniques of running casing, cementing, down-hole perforating, running the screen jacket assembly and then gravel packing with a cross-over tool. The perforating operation is particularly expensive and can be dangerous since explosives are typically used to form the perforations. Furthermore, it is the usual practice to form a total of only about twelve 3/4" perforations per foot of casing length. The relatively few number of holes and their large size sometimes tends to produce voids or "holidays" in the later installed sand-controlling gravel pack since a much greater flow velocity exists than would be the case if many more perforations were present. The problem of voids in the gravel pack and consequent failure when the fine formation material moves right into the screen and erodes it is especially great when the hole is highly deviated.
Prepack screen assemblies have been manufactured in the past which include a uniform consolidated or unconsolidated annulus of resin-coated sand or gravel which fills the space between a pair of concentric screen members. They are typically used with an external gravel pack since formation sand would plug their slots. If used in a deep hole, such assemblies could not be easily removed in the event of a failure of the internal annular gravel pack since the prepack screens are typically made of stainless steel which would be difficult to cut through with a wash-over tool. Furthermore, they would probably tear apart and jam as the wire and rod of which they are made comes apart.
The resin-coated gravel or sand used in the aforementioned prepack screen assemblies is preferably of the type described in an article entitled, "Performance Review of Phenolic-Resin Gravel Packing" by Lowell W. Saunders and Howard L. McKinzie which appeared in the February 1981 issue of "JOURNAL OF PETROLEUM TECHNOLOGY" at pages 221-228. Although such gravel has been supplied as part of a precured packing between two concentric well screens, it is usually used as a direct replacement for ordinary gravel packs which are formed in situ. The gravel is supplied in loose form from bags and is cured after installation by the relatively high temperatures in the well. The cured resin-coated gravel is inert to acid but is soluble in basic fluids having a high pH. The latter property makes it simple to easily remove the packing at any time. Another article describing the uses of uncured resin-coated sand and various environments in which it can be used is Paper No. SPE 7004 of A. Richard Sinclair and John W. Graham entitled, "An Effective Method of Sand Control." The paper was presented at a meeting of the Society of Petroleum Engineers of AIME in Lafayette, La. on Feb. 15-16, 1978.